1. Field of the Invention
This invention relates to a magnetic roll to be used for magnetic brush development mainly in electrostatic recording devices such as copying machines, facsimiles, and printers and to a method for the manufacture of the magnetic roll.
2. Description of the Prior Art
The magnetic brush development in an electrostatic recording system is accomplished by mounting a sleeve of non-magnetic substance on the outer surface of a magnetic roll incorporating permanent magnets, causing a developing agent such as a magnetic toner to adhere to the periphery of the sleeve thereby forming a magnetic brush, then allowing the sleeve to move relative to a photosensitive material thereby causing the produced electrostatic latent image to be rubbed against the photosensitive material.
For the sake of the magnetic brush development described above, there has been conventionally used a magnetic roll which has a plurality of disk retaining flanges fastened to the periphery of a roll shaft and a plurality of bar-shaped sintered ferrite magnets of alternately opposed poles held in position on the retaining flanges.
The magnetic roll of this construction, however, is required to meet certain level of accuracy with respect to the attachment of the magnets. In the manufacture of this magnetic roll, therefore, particularly the work of attaching the retaining flanges to the roll shaft and the work of attaching the magnets to the retaining flanges call for very much time and labor. Besides, the fastening of the magnets to the retaining flanges with an adhesive agent is difficult to achieve. The magnetic roll as a whole is complicated in construction, heavy, and difficult to handle. Moreover, it is costly.
Various improvements intended to overcome the disadvantages mentioned above have been proposed. See, e.g., Japanese Utility Model Application Disclosure No. 16905/1981, etc. They are, however, not free from problems.
Japanese Patent Application Disclosure No. 100581/1980 teaches a magnetic transfer roll having a layer of elastic substance formed on the periphery of a roll shaft and a layer of magnetic substance formed on the periphery of the layer of elastic substance. Since the magnetic transfer roll is required to deform while the magnetic transfer is in process, it necessitates use of the elastic layer which is formed of a soft, resilient substance such as sponge. The flexible, elastic layer, however, is not believed to retain magnets such as sintered magnets in position with high accuracy.
The prior art of this invention further embraces U.S. Pat. Nos. 3,364,545, 3,457,618, 3,945,343, and 4,155,328, for example.